Fifteen percent of older people cannot sleep past 5 am, and twice as many older people complain they wake up too early at least several times per week. We have found that in healthy older people this earlier timing of awakening is neither a consequence of an-related shortening of the intrinsic period of the circadian pacemaker driving these rhythms nor of a change in resetting response to light. Our preliminary data suggests the early awakenings in older may be related to a reduced homeostatic drive for sleep. Based on our results, four testable hypotheses are proposed: 1) Older people carry a substantial sleep debt despite subjective self reports of an inability to sleep more than 5-7 hours per day. 2) In older people the dose-response relationships between measures of sleep continuity and homeostasis [sleep duration, sleep efficiency and electroencephalographic (EEG) slow-wave activity)] and the preceding duration of wakefulness follow exponential saturating function when wakefulness is varied from 8 to 56 hours. 3) The duration of waking required to elicit a given improvement in sleep continuity or a given intensity of hours. 3) The duration of waking required to elicit a given improvement in sleep continuity or a given intensity of EEG slow-wave activity is greater in older people than in young adults. 4) Objective measures will reveal less impairment of wake-time alertness and performance after sleep deprivation in older individuals than in younger. We propose to test these hypotheses in assessments of the dose-response relationships between the duration of wakefulness and the homeostatic drive for sleep in older and young subjects who have been sleep satiated. The homeostatic drive for sleep will be quantified in a protocol in which individuals will be sleep satiated, then have episodes of wakefulness of varying duration (8, 16, 32, or 56 h), followed by recovery sleep scheduled for 44 hours during a 60-h time window. During all scheduled sleep episodes, sleep-wake state will be assessed polysomnographically and all EEG recordings will be subjected to spectral analysis. This work has significant implications for geriatric medicine and aims at answering a fundamental aspect of age-related changes in sleep regulation. Sleep disorders in the elderly are an important causes of diminished quality of life in otherwise healthy people, often leading to an overuse of sleep medications with unfortunate physiological and psychological side effects. If reduced homeostatic drive is contributing to the sleep problems of older persons, than effective counter-measures can be designed. Greater understanding of the mechanisms contribution to sleep complaints in the elderly and development of practical, non- pharmacological treatment methods offer substantive promise for improved health of the elderly.